Brain acetylcholinesterase (AChE) forms stable complexes with amyloid-␤ peptide (A␤) during its assembly into filaments, in agreement with its colocalization with the A␤ deposits of Alzheimer's brain. The association of the enzyme with nascent A␤ aggregates occurs as early as after 30 min of incubation. Analysis of the catalytic activity of the AChE incorporated into these complexes shows an anomalous behavior reminiscent of the AChE associated with senile plaques, which includes a resistance to low pH, high substrate concentrations, and lower sensitivity to AChE inhibitors. Furthermore, the toxicity of the AChE-amyloid complexes is higher than that of the A␤ aggregates alone. Thus, in addition to its possible role as a heterogeneous nucleator during amyloid formation, AChE, by forming such stable complexes, may increase the neurotoxicity of A␤ fibrils and thus may determine the selective neuronal loss observed in Alzheimer's brain.

Acetylcholinesterase (AChE) molecular forms were studied during mouse brain development. Mouse embryos expressed a monomeric (G1) and a tetrameric (G4) AChE form. Our results indicate that G4 AChE expressed at embryonic day (ED) 9 and ED15 could be purified by acridinium-Sepharose chromatography and shared similar biochemical and kinetic properties with the adult form. However, the G1 form expressed at either embryonic stage did not bind to acridinium, was not inhibited by excess substrate, and possessed higher K(m) and lower Vmax values than the adult G1 form. Two peripheral anionic binding site inhibitors, fasciculin and propidium, had a significantly lower affinity for the monomeric form at ED9. Results are discussed in terms of the biological significance of the embryonic G1 form, and its resemblance to the AChE activity found, associated with the senile plaques present in the brains of Alzheimer's patients.

In order to learn about factors that influence the reproductive cycle of marine bivalves, the levels of prostaglandins (PGs) PGE 2 and PGF 2α were measured during gametogenesis in the functional hermaphrodite scallop, Argopecten purpuratus. The PGs, in extracts of gonads of these scallops, were measured by radioimmunoassay techniques on different days after an induced spawning. To verify that gametogenesis was taking place during the experimental time, each time scallops were sampled, gonadal maturation was examined by gonadal index and by qualitative and quantitative histological analysis. Quantitative analysis involved oocyte size frequency distributions and determination of cross-sectional area occupied by mature sperm. The experiment was run twice, once in winter and once in spring. A linear decrease of both PGs was detected in male and female portions of the gonads as the maturation of these proceeded. In the spring experiment, this decrease was detected in both gonadal portions, but in the winter experiment, it was detected only for the male portion and not for the female one. The histological analysis of the gonads showed that in winter, the female gametes did not mature, although the male gametes did. These results are indicative of an inverse relationship between gonadal maturity and PG levels.

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Collagen-tailed asymmetric acetylcholinesterase (AChE) forms are believed to be anchored to the synaptic basal lamina via electrostatic interactions involving proteoglycans. However, it was recently found that in avian and rat muscles, high ionic strength or polyanionic buffers could not detach AChE from cell-surface clusters and that these buffers solubilized intracellular non-junctional asymmetric AChE rather than synaptic forms of the enzyme. In the present study, asymmetric AChE forms were specifically solubilized by ionic buffers from synaptic basal lamina-enriched fractions, largely devoid of intracellular material, obtained from the electric organ of Torpedo californica and the end plate regions of rat diaphragm muscle. Furthermore, foci of AChE activity were seen to diminish in size, number, and staining intensity when the rat synaptic basal lamina-enriched preparations were treated with the extraction buffers. In the case of Torpedo, almost all the AChE activity was removed from the pure basal lamina sheets. We therefore conclude that a major portion of extracellular collagen-tailed AChE is extractable from rat and Torpedo synaptic basal lamina by high ionic strength and heparin buffers, although some non-extractable AChE activity remains associated with the junctional regions.The enzyme acetylcholinesterase (AChE) 1 plays a key role in cholinergic neurotransmission (1). Its predominant form at the neuromuscular junction is the collagen-tailed asymmetric form, A 12 , which is located on the extracellular surface positioned for the hydrolysis of acetylcholine. Most of this junctional AChE is associated with the basal lamina (BL), located between the nerve ending and the muscle plasma membrane (2, 3), and can be removed from the cell surface of muscle tissue (4, 5) and mouse myotubes (6) by treatment with collagenase, indicating that the collagenic tail of the enzyme is involved in its anchorage to the BL (7,8). Although the precise mechanisms by which asymmetric AChE forms are anchored to the BL remain elusive (9), there is compelling evidence to suggest that heparan sulfate proteoglycans (HSPGs) or related proteoglycans are involved (7,10). This evidence includes the recent finding that A 12 has two heparin-binding consensus sequences in its collagenic tail (11). Asymmetric AChE forms have a high binding affinity for BL components, particularly HSPGs (12) which are themselves major constituents of basement membranes (13,14). Heparin and heparan sulfate have also been shown to release asymmetric AChE activity from rat muscle end plate regions (15) and BL sheets purified from the electric organ of Discopyge (16). The demonstration that A 12 could bind and be selectively eluted from heparin-agarose columns, whereas non-collagenous forms and A 12 after collagenase treatment could not, proved the direct interaction of A 12 with heparin in vitro (11,17). Direct interactions with heparin/heparan sulfate moieties in vivo have also been demonstrated. Asymmetric AChE forms were shown to bind the surface of HSPGri...